When Marshall orders the comically large bottle of champagne, the barman starts taking it off of the bar before the guys and Wendy the Waitress even reach the bar.
At about 13:14 at the Apartment- While talking to Barney, you can see Robin holding her purse over her shoulder. She proceeds to take the purse off her shoulder when the camera goes to Ted. When the camera goes back to Robin her purse is back on her shoulder and she then takes it off again.
The social security number that Lily gives the mortgage broker is only 8 numbers long while a real social security number is 9 numbers long.
Robin claims that the highest mountain peak in Canada is Mt. Waddington. The highest peak in Canada is Mt. Logan in Yukon Territory. Mt. Waddington is only the highest peak in British Columbia, the province Robin hails from.